Method of obtaining a sialon-based ceramic material by reducing an aluminosilicate material, and use thereof in forming a ceramic coating on a refractory substrate

Abstract

A ceramic material based on Sialon, in particular on β'-Sialon is obtained by reducing an aluminosilicate precursor by means of a gas phase comprising a mixture of hydrogen and nitrogen doped with a gaseous carbon compound. The gaseous carbon compound is a gas containing carbon in combined form, e.g. an alkane, and its concentration by volume in the gas is less than 3%. The method is particularly suitable for forming Sialon-based coatings on substrates that are solid or fibrous. For composite materials constituted by a fiber preform densified by means of a matrix, the method can be used to form an interphase coating on the fibers of the preform prior to densifying the preform, or the method can be used to form a matrix that is based on Sialon.

We claim: 
     
       1. A method of obtaining a Sialon-based ceramic material, comprising the steps of providing an aluminosilicate material and reducing said aluminosilicate material, wherein the aluminosilicate material is reduced by a gas phase comprising a mixture of hydrogen and of nitrogen doped with a gaseous carbon compound, with said aluminosilicate material remaining substantially free of solid elemental carbon. 
     
     
       2. The method according to claim 1, wherein said aluminosilicate is reduced by a gas phase containing the gaseous carbon compound at a concentration of less than 3% by volume. 
     
     
       3. A method according to claim 1, wherein the gaseous carbon compound is a hydrocarbon. 
     
     
       4. A method according to claim 1, wherein the gaseous carbon compound is an alkane. 
     
     
       5. A method according to claim 1, wherein the volume ratio of hydrogen to nitrogen in the gas lies in the range 1/10 to 10/1. 
     
     
       6. The method according to claim 1, wherein said reducing step is carried out at a temperature of not less than 1100° C. 
     
     
       7. The method according to claim 1, wherein said reducing step is carried out by placing the aluminosilicate material in an enclosure and admitting into said enclosure a flow of gas comprising said mixture of hydrogen and of nitrogen and said gaseous carbon compound. 
     
     
       8. A method according to claim 1, wherein said reducing step is carried out by placing the aluminosilicate material in an enclosure, admitting into said enclosure a flow of gas comprising said mixture of hydrogen and nitrogen, and providing a carbon-containing solid material on the path of said gas flow inside the enclosure, upstream of the aluminosilicate material, whereby said gaseous carbon compound is produced by chemical reaction between hydrogen from the gas flow and the carbon-containing solid material. 
     
     
       9. The method according to claim 1, wherein said aluminosilicate material is clay. 
     
     
       10. The method according to claim 1, wherein said aluminosilicate material is in powder form. 
     
     
       11. The method according to claim 10, wherein said aluminosilicate material comprises a mixture of silica and alumina powders. 
     
     
       12. The method according to claim 1, wherein said aluminosilicate material is provided in the form of an aluminosilicate fiber. 
     
     
       13. The method of forming a Sialon-based ceramic coating on a refractory substrate, comprising the steps of: providing an aluminosilicate material in suspension in a liquid vehicle;   depositing the suspension on the substrate;   eliminating the liquid vehicle; and   reducing the aluminosilicate material by a gas phase comprising a mixture of hydrogen and of nitrogen doped with a gaseous carbon compound, with said aluminosilicate material remaining substantially free of solid elemental carbon.   
     
     
       14. The method of forming a Sialon-based ceramic coating on fibers of a refractory fiber substrate, comprising the steps of: providing an aluminosilicate material in suspension in a liquid vehicle;   impregnating the fiber substrate with the suspension;   eliminating the liquid vehicle; and   reducing the aluminosilicate material by a gas phase comprising a mixture of hydrogen and of nitrogen doped with a gaseous carbon compound, with said aluminosilicate material remaining substantially free of solid elemental carbon.   
     
     
       15. The method according to claim 14, wherein the steps of impregnating the fiber substrate, eliminating the liquid vehicle and reducing the aluminosilicate material are repeated. 
     
     
       16. The method according to claim 14, wherein the aluminosilicate material is a clay having a scaly structure. 
     
     
       17. The method according to claim 14, wherein the aluminosilicate material is kaolinite.